Olefin metathesis is a well-known process wherein one or more olefinically-unsaturated reactants are contacted with a metathesis catalyst under reaction conditions sufficient to cleave one or more of the carbon-carbon double bond(s) in the olefinically-unsaturated reactant(s), after which the resulting molecular fragments are reformed into one or more olefinically-unsaturated products that are different from the olefinically-unsaturated reactant(s). The prior art teaches various classes of olefin metathesis processes including self-metathesis (SM), cross-metathesis (CM), acyclic ring-closing or cyclization metathesis (RCM), ring-opening polymerization metathesis (ROMP), and polymer segment interchange metathesis (PSIM).
Recent interest in olefin metathesis chemistry has led to a number of published patent applications. For example, WO 2008/027267 A2 relates to production of metathesis products by high melting polymer segment interchange. WO 2008/027268 A2 relates to production of metathesis products by amorphous polymer segment interchange. WO 2008/027269 A2 relates to production of telechelic compounds by metathesis depolymerization. WO 2008/027283 A2 relates to production of meta-block copolymers by polymer segment interchange. WO 2009/0091588 A2 relates to metathetic production of functionalized polymers.
Many prior art catalysts are single component catalysts consisting of a single site ruthenium-ligand complex comprising one ruthenium atom, a plurality of anionic and/or neutral ligands, for example, halide(s) and phosphine(s) ligands, and one carbene (alkylidene) group of formula: CRaRb bonded to the ruthenium atom, wherein Ra and Rb are independently selected from hydrogen and C1-C20 hydrocarbyl groups. Single site ruthenium complex-catalyzed metathesis processes are illustrated in the following prior art references: WO 96/04289, U.S. Pat. No. 7,102,047, and Thomas Weskamp, et al., Angewandte Chemie Int. Ed., 1999, 38, pp. 2416-2419. Single site ruthenium complex catalysts tend to exhibit decreased activity at elevated temperatures, for example, at temperatures greater than 90° C.
Other prior art references disclose the use of bimetallic catalysts or bimetallic catalyst precursors in metathesis processes. These catalysts or catalyst precursors include homo-bimetallic ruthenium complexes containing two ruthenium atoms and hetero-bimetallic complexes containing one ruthenium atom and a different metallic atom, such as Ti or W. Terminal ligands on each of the metal atoms include one or more anionic and/or neutral ligands, such as halide(s) and/or phosphine(s); whereas ligands bridging the two metal atoms embrace many diverse species including halides, dithiolates, phosphine-substituted cyclopentadienyl, or bisalkylidene-substituted phenyl groups. These bimetallic metal complexes generally do not contain a metal-metal bond, but contain instead two discrete metal centers within a single complex. Where the bimetallic complex comprises one or more alkylidene ligands bonded to one of the ruthenium atoms, no other catalytic component is required. Where the bimetallic complex comprises no alkylidene ligand bonded to a ruthenium atom, then the complex may be considered to be a catalyst precursor, and a co-catalyst is usually required. The co-catalyst is advantageously a carbene or alkylidene-generating agent, such as a propargyl compound.
The following prior art references illustrate a variety of homo and hetero bimetallic metathesis catalysts and catalyst precursors: Eric L. Dias, et al., Organometallics, 1998, 17, pp. 2758-2767; Kay Severin, Chem. Euro. J., 2002, 8, pp. 1515-1518; Salai Cheettu Ammal, et al, Journal of the American Chemical Society, 2005, 127, pp. 9428-9438; Pierre Le Gendre, et al., Journal of Organometallic Chemistry, 2002, 643-644, pp. 231-236; and Jérôme Goux, et al., Journal of Organometallic Chemistry, 2005, 690, pp. 301-306; Marcus Weck, et al., Macromolecules, 1996, 29, pp. 1789-1793, as well as previously cited WO-A1-96/04289.
Other prior art references, such as Munetaka Akita, et al., Journal of Organometallic Chemistry, 1998, 569, pp. 71-78, teach carbon-carbon coupling from labile diruthenium bridging μ-methylene complexes. Other references teach crystallographic structures or various reactivities of diruthenium bridging μ-alkylidene or μ-hydrido complexes. See, for example, Andrew A. Cherkas, Organometallics, 1987, 6, pp. 1466-1469; Manfred Jahncke, et al., Organometallics, 1997, 16, pp. 1137-1143; and Mathieu J.-L. Tschan, et al., Organometallics, 2005, 24, pp. 1974-1981.
Despite various disclosures to date, the art would benefit from the discovery of new ruthenium metathesis catalysts, particularly, those having an improved reactivity at higher operating temperatures, preferably, greater than about 90° C. Operation at higher temperatures affords faster reaction rates and easier removal of solvent(s) employed in the process, by reducing temperature cycling between the metathesis operating temperature and the temperature needed for solvent separation.